In recent years, low-power displays with high image quality have been in increasing demand, as various electronic apparatuses such as a mobile phone and a personal digital assistance (PDA) have become widespread. Above all, recently, as electronic book delivery businesses have started, displays for the purpose of reading character information for a long time have been receiving attention and therefore, a display unit having display quality suitable for that purpose has been desired.
For reading purpose, display units of a cholesteric liquid crystal type, an electrophoretic type, an electric redox type, a twisting ball type, and the like have been proposed. Above all, the reflection-type display units may be preferable. This is because bright display is performed using reflection (diffusion) of outside light in a manner similar to that of paper and therefore, display quality close to that of paper is achieved. In addition, this is also because backlight is unnecessary and therefore, power to be consumed is suppressed.
A strong candidate of the reflection-type display units is an electrophoretic display unit that effects light and shade (contrast) using an electrophoretic phenomenon. This is because power to be consumed is low, and high-speed responsiveness is superior. Therefore, various studies have been made for a display method of the electrophoretic display unit.
Specifically, there has been proposed a method in which two kinds of charged particles, which have different optical reflection properties and polarity, are dispersed in insulating liquid, and the charged particles are moved utilizing the difference in polarity (for example, see Patent Literatures 1 and 2). In this method, distributions of the two kinds of charged particles are changed in response to an electric field and therefore, contrast is effected utilizing the difference in optical reflection properties.
Further, there has been proposed a method in which charged particles are dispersed in insulating liquid, and using a porous layer having optical reflection properties different from those of the charged particles, the charged particles are moved through pores of the porous layer (for example, see Patent Literatures 3 to 6). This porous layer is a polymeric film in which pores are formed by perforation processing with a laser, a cloth woven of synthetic fibers and/or the like, an open-cell foam porous polymer, or the like. In this method, positions of the charged particles are changed in response to an electric field and therefore, contrast is effected utilizing the difference in optical reflection properties.